In the transformer coil art, a number of methods have been adapted for holding or anchoring the turns of an electrical coil, so that they can resist movement when the turns are subjected to a flow of current and consequent electromagnetic forces tending to move them out of position.
Discontinuously patterned, resin coated kraft paper has been used as a very effective restraint, to provide porous solidification of transformer coils. Ford, in U.S. Pat. No. 3,246,271, applied the resin pattern by a solution impregnation method, and Croop et al., in U.S. Pat. No. 3,974,302, applied the resin pattern by an electrostatic coating technique. Both methods employ ovens to cure the applied resin.
Kraft paper as purchased contains about 4 wt.% to 15 wt.%, generally about 7 wt.%, moisture. After passing through ovens, with temperatures of up to 250.degree. C., in order to "B"-stage the applied resin, the moisture content of the paper is reduced to about 2 wt.%. The paper tends to become inflexible and brittle below 3.5 wt.% moisture content and may, in some instances, break during the coil winding process, requiring stoppage and rewinding. What is needed is a method to either replace the lost moisture or apply a resin pattern and "B"-stage by a technique which does not cause loss of moisture below 3.5 wt.%.